Rapid advances in the field of solid state technology are continuously reducing the size of various electronic devices, including computers, video games, and calculators. The size to which such devices can be reduced nevertheless is limited by the size of the output display devices that are generally required to properly utilize these devices. This limitation has arisen primarily because the display devices must have sufficient resolution to display at least a full page of textual information. In order to achieve this resolution, commonly used display devices, such as cathode ray tubes and liquid-crystal displays, must be of sufficient size so that a user can adequately view several hundred thousand picture elements on the display device. Accordingly, it generally difficult and expensive to reduce the dimensions of such display devices to a significant degree without significantly sacrificing resolution.
There are times, however, when the use of a relatively large and heavy display device is inconvenient. Much smaller display devices have thus been designed to provide a visual display that is comparable in resolution to larger display devices known in the art. One such device is described in U.S. Pat. No. 4,934,773, to Becker, which discloses a miniature display device that can either be hand-held or mounted on a headstrap. When looking into the device, a user views a two-dimensional virtual image. The virtual image is created by a linear array of light-emitting diodes ("LEDs") which generates a line image. A two-dimensional virtual image is formed from the line image by reflecting the line image from an oscillating mirror to the user's eye. As the mirror oscillates, the line image is swept back and forth to generate a rectangular two-dimensional raster. By properly timing the "on" and "off" timing of the LEDs, an image is produced.
However, although the device can easily produce a monochrome image using single color LEDs in the linear array, there is some difficulty producing a full-color image (i.e. an image that includes at least the three additive primary colors red, blue and green). The Becker patent provides a solution to this problem by teaching a second embodiment that produces a full-color display. This display uses three LED arrays, which each require separate hardware and software for proper operation, and that respectively emit red, blue, and green beams of light.
The latter device has limitations. First, the overall size of the device is increased, however, because it must include at least the three LED arrays, as well as the hardware and software that accompanies those arrays. The desired miniaturization effect consequently is limited as the overall manufacturing cost of the device is increased.
Additional problems arise when three LED arrays are used to produce a full-color image. For example, it is known in the art that normal chromatic aberrations in a lens can tend to distort an image if the distance between at least two of the beams forming the image is relatively large (typically on the order of 1 mm) as they intersect the incident surface of the lens.
Further, it is also known in the art that any LED array in such a display system will typically have at least a 1 mm space on at least one side of it so that the array can be properly coupled to a connecting substrate. Consequently, any adjacent grouping of at least three LED arrays will necessarily have at least one array that is separated from the other arrays by at least 1 mm. Image distortion may therefore occur, which is a highly undesirable result in such systems.
One solution to the latter problems is to position the LED arrays in different physical locations and coincidentally re-align the beams with reflecting mirrors. Such a configuration nevertheless requires additional elements, again increasing the size and cost of the device.
Alternatively, it is possible to make a color display with only two additive primary colors using two single color LED arrays. The color gamut possible with only two primary colors, however, is extremely limited and such a display would not be suitable for various photorealistic applications such as CAMCORDER viewfinders or television displays. These color sensitive applications need a large color gamut that requires at least three additive primaries to achieve a large color gamut.
Other full-color miniature display devices utilize liquid crystal displays that function generally identically to the liquid crystal displays commonly used in larger scale full-color display devices. Such full-color miniature display devices typically have a large number of very closely spaced miniature pixels that are either red, green, or blue. The pixels are selectively lit to produce a full-color display. Such devices, however, tend to be relatively expensive and often require sophisticated hardware and software to drive them.
Accordingly, there is a need for a miniature display device that provides a full-color visual display, has a relatively low manufacturing cost, and is more compact than those related full-color display devices known in the art.